1. Field of the Invention
The present invention relates generally to oxygen corrosion inhibitors. More particularly, the present invention relates to a composition for inhibiting the oxygen corrosion of metal surfaces in liquid systems. Still more particularly, the present invention relates to an oxygen scavenging composition, and a method of using such composition, for the control of metal corrosion in steam generating systems, and the like.
2. Description of the Prior Art
The presence of dissolved oxygen in water sustains the corrosion of iron and steel especially under heat transfer conditions such as are found, for instance, in steam generation and similar processes. In order for such processes to function ideally, therefore, it is necessary to remove oxygen from such aqueous systems so as to maintain the oxygen concentration at an optimal minimum level, a necessity that becomes more critical the larger the generating system and the higher the operating pressure become. The major portion of dissolved oxygen is removed from steam generating systems, especially large and complex systems, by mechanically treating the makeup water stream, as well as the recycle condensate stream, in a deaerating feedwater heater situated upstream of the steam boiler. Even under optimum operating conditions, however, it is usually not possible to mechanically reduce the oxygen concentration below 0.007 ppm. It has been the practice, therefore, to augment mechanical oxygen reduction with a chemical reduction treatment so as to further reduce the oxygen concentration to a minimum level that is usually selected on the basis of economic considerations.
Sodium sulfite has long been used in chemical treatment of oxygen-bearing steam boiler water, particularly in low and medium pressure steam generating systems. Its use, however, is generally avoided in high pressure systems because carryover to the steam turbines caused by dissolved solids concentration, e.g., sulfite residual and by-product sodium sulfate, increases with pressure. A second reason is the possibility of thermal breakdown of the sodium sulfite to corrosive sulfur dioxide and hydrogen sulfide. Accordingly, hydrazine, the reaction products of which are inert and do not add to the dissolve solids content of the boiler water, has generally been employed as an oxygen scavenger in high pressure steam generating systems. The advantages of hydrazine, moreover, have been extended to low and medium pressure systems, in which its rate of scavenging action had been too slow for commercial adaptation, by the use of catalysts such as, for example, certain pyrazolidones and aminophenols as disclosed in U.S. Pat. No. 3,728,281. These compounds have the effect of speeding up the rate of scavenging action of hydrazine. Notwithstanding these advantages of hydrazine as an oxygen scavenger, it has, nevertheless, the disadvantage of requiring special handling because it is toxic.
Various other materials and compositions have been proposed, from time to time, as oxygen scavengers or oxygen corrosion inhibitors for use in steam generating systems, secondary oil well recovery systems and other types of corrosive liquid systems. U.S. Pat. No. 3,625,888 suggests, for example, the use of a carbonylbisulfite addition product in combination with a small amount of a transition metal, such as cobalt, as being particularly suited for use as a corrosion inhibitor in oil well water-flooding procedures. Various amine alcohols disclosed as novel in U.S. Pat. No. 3,954,873 are suggested as useful as metal corrosion inhibitors. A composition comprising a hydrazine compound, e.g., a mono- or dialkyl hydrazine, and a saturated or unsaturated organic acid, e.g., an alkyl acid of 3-26 carbon atoms, is disclosed in U.S. Pat. No. 3,629,111 as a corrosion inhibitor in hydraulic fluids designed for fluid pressure operating devices. U.S. Pat. No. 3,962,113 discloses mono-, di- and trialkyl hydrazines as oxygen scavengers particularly adapted for use in steam generating systems, while U.S. Pat. No. 3,983,048 discloses similar oxygen scavengers used in combination with aryl amines. Other hydrazine-based oxygen scavenging compositions are disclosed in U.S. Pat. Nos. 4,192,844 and 4,238,349, while hydroquinone, hydroxylamines and carbohydrazide are disclosed as oxygen scavengers for use in steam generating systems in U.S. Pat. Nos. 4,278,635; 4,067,690 and 4,269,717, respectively.